A laboratory study of the effect of Fe(II)-bearing minerals on nuclear magnetic resonance (NMR) relaxation measurements

Geophysics ◽  
2010 ◽  
Vol 75 (3) ◽  
pp. F71-F82 ◽  
Author(s):  
Kristina Keating ◽  
Rosemary Knight
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Relaxation Rate ◽  
Nmr Relaxation ◽  
Relaxation Mechanism ◽  
Surface Relaxation ◽  
Fast Diffusion ◽  
Relaxation Rates ◽  
Bulk Fluid ◽  
Surface Relaxivity ◽  
Diffusion Relaxation

A laboratory study was conducted to measure the effect of the mineralogic form and concentration of iron(II) [Fe(II)] minerals on nuclear magnetic resonance (NMR) relaxation rates of water-saturated sand mixtures. We measured mixtures of quartz sand and three common Fe(II)-bearing minerals in granular form: siderite [Formula: see text], pyrite [Formula: see text], and pyrrhotite ([Formula: see text]; [Formula: see text]) at two concentrations of iron by weight. The NMR response of these samples was used to calculate four transverse relaxation rates for each Fe(II) mineral mixture: total mean log, bulk fluid, diffusion, and surface relaxation rates. The surface area of the samples was used to calculate the surface relaxivity of the sample and the magnetically active surface. For each iron mineral, the mean log and surface relaxation rates were greater for samples with higher Fe(II) concentration. For the siderite,pyrrhotite, and high-concentration pyrite mixtures, surface relaxation was the dominant relaxation mechanism. Bulk fluid relaxation contributed significantly to the total relaxation for the siderite and pyrite mixtures; for the low-concentration pyrite mixtures, bulk fluid relaxation was the dominant relaxation mechanism. For the pyrrhotite mixtures, the diffusion relaxation rate was nonzero and slower than the surface relaxation rate; for the siderite and pyrite mixtures, the diffusion relaxation rate was zero. Surface relaxivity calculations revealed that, for the pyrite mixtures, relaxation occurred in the fast diffusion regime; for the siderite and pyrrhotite mixtures, relaxation did not occur in the fast diffusion regime. The range of surface relaxivity values calculated depends on mineralogic form. We conclude that Fe(II) concentration and mineralogic form are important factors in determining relaxation rate.

A laboratory study to determine the effect of iron oxides on proton NMR measurements

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. E27-E32 ◽  
Author(s):  
Kristina Keating ◽  
Rosemary Knight
Keyword(s):  
Iron Oxide ◽  
Relaxation Rate ◽  
Iron Oxides ◽  
Quartz Sand ◽  
Pore Space ◽  
Nmr Relaxation ◽  
Volume Ratio ◽  
Proton Nuclear Magnetic Resonance ◽  
Surface Relaxation ◽  
Relaxation Rates

Using laboratory methods, we investigate the effect of the presence and mineralogic form of iron on measured proton nuclear magnetic resonance (NMR) relaxation rates. Five samples of quartz sand were coated with ferrihydrite, goethite, hematite, lepidocrocite, and magnetite. The relaxation rates for these iron-oxide-coated sands saturated with water were measured and compared to the relaxation rate of quartz sand saturated with water. We found that the presence of the iron oxides led to increases in the relaxation rates by increasing the surface relaxation rate. The magnitude of the surface relaxation rate was different for the various iron-oxide minerals because of changes in both the surface-area-to-volume ratio of the pore space, and the surface relaxivity. The relaxation rate of the magnetite-coated sand was further increased because of internal magnetic field gradients caused by the presence of magnetite. We conclude that both the concentration and mineralogical form of iron can have a significant impact on NMR relaxation behavior.

The effect of spatial variation in surface relaxivity on nuclear magnetic resonance relaxation rates

Geophysics ◽  
2012 ◽  
Vol 77 (5) ◽  
pp. E365-E377 ◽  
Author(s):  
Kristina Keating ◽  
Rosemary Knight
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Rate ◽  
Quartz Sand ◽  
Weak Coupling ◽  
Nmr Relaxation ◽  
Coupling Region ◽  
Surface Relaxivity ◽  
Nmr Data ◽  
The Relationship

Nuclear magnetic resonance (NMR) relaxation measurements are sensitive to the physiochemical environment of water in saturated porous media and can provide information about the properties of geologic material. Interpretation of NMR data typically relies on three assumptions: that pores within the geologic material are effectively isolated such that the diffusion of a proton between pores is limited (i.e., there is weak coupling); that relaxation occurs in the fast-diffusion regime; and that surface relaxivity [Formula: see text] is uniform throughout the measured volume. We investigated the effect of spatial variation in [Formula: see text] on the NMR relaxation measurement and evaluated two equations relating [Formula: see text] to the NMR relaxation rate for samples containing two types of surfaces, each with a different surface relaxivity. One equation was valid when there is weak diffusional coupling between pores, the other is valid when there is strong diffusional coupling. We prepared a suite of samples composed of quartz sand and an iron-coated quartz sand. NMR relaxation occurred in two distinct regions: the weak- and strong-coupling regions. In the weak-coupling region, the equation did not accurately represent the relationship between the two [Formula: see text] values and the NMR relaxation rate, suggesting that further research is required to understand the effect of spatially variable [Formula: see text] in this relaxation region. In the strong-coupling region, the equation accurately represented the relationship between the two values of [Formula: see text] and the NMR relaxation rate. The results from these laboratory experiments represented a first step towards accounting for spatial variability in [Formula: see text] in the interpretation of NMR data.

Quantifying the Mechanisms Contributing to Nuclear-Magnetic-Resonance Surface Relaxation of Protons in Kerogen Pores of Organic-Rich Mudrocks

SPE Journal ◽  
2019 ◽  
Vol 24 (06) ◽  
pp. 2438-2457 ◽  
Author(s):  
Saurabh Tandon ◽  
Zoya Heidari
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Numerical Simulations ◽  
Dipolar Coupling ◽  
Surface Relaxation ◽  
Pore Scale ◽  
New Model ◽  
Surface Relaxivity ◽  
Coupling Mechanisms ◽  
Organic Pores

Summary The evaluation of nuclear–magnetic–resonance (NMR) measurements can be challenging in organic–rich mudrocks because of their heterogeneity, tight pores, presence of kerogen, and the lack of understanding regarding the relaxation mechanism on the kerogen surface. Numerical simulation of NMR responses in the pore–scale domain in such complex rocks is also not very useful because most of the inputs are derived from conventional surface–relaxivity models. The conventional grain/fluid–interaction models for quantifying surface relaxivity do not account for any dipolar coupling in kerogen pores. The objectives of this paper are to develop a new surface–relaxivity model that accurately accounts for homonuclear dipolar coupling in kerogen pores; to introduce a pore–scale simulation method for reliable modeling of NMR response; and to quantify the effects of applying the new relaxivity model on simulated NMR responses and phase saturations. We start by considering the generalized Langmuir adsorption (GLA) theory for the adsorption of hydrocarbons on the surfaces of organic pores in mudrock samples. We used this adsorption model and the anisotropic rotation of molecules to develop a new surface–relaxivity model that accurately quantifies both transverse (T2) and longitudinal (T1) relaxation of protons in kerogen pores. The new model was used to simulate NMR responses in ellipsoidal pores and segmented focused–ion–beam scanning–electron–microscope (FIB–SEM) images of organic–rich mudrock samples using a pore–scale finite–volume simulation technique. The inputs to the simulator are the previously discussed pore geometries and the bulk and surface properties of different fluids present in the pore space. The outputs from the simulator were T2 and T1 decay constants in the previously mentioned pore geometries. The results of NMR simulations are then used to quantify the sensitivity of NMR responses to surface relaxivities computed using different models and NMR–based estimates of adsorbed–hydrocarbon volume. The results obtained from the new model verified that intramolecular coupling dominates the T1 and T2 surface relaxivities at high correlation times (greater than 1×10–7 seconds), which are usually observed for hydrocarbons in kerogen pores. The new model also confirmed the observation that NMR responses in mudrocks are not a function of kerogen thermal maturity but strongly depend on kerogen type. The results of numerical simulations demonstrated that dominant T2 peaks, T1–T2 ratios, and estimated adsorbed fractions are functions of molecular correlation time. Numerical simulations of NMR responses in organic–rich mudrock demonstrated that misidentifying coupling mechanisms could cause errors of up to 40.9 and 57.3% in estimates of adsorbed–hydrocarbon volume calculated using T2 and T1–T2 measurements, respectively. The surface–relaxivity model developed in this paper is more reliable than the previously published relaxivity models because it includes the effects of different coupling mechanisms on surface relaxation in organic pores. The new model can be reliably extended for quantifying surface relaxivity at higher temperatures and for different fluids, which enables interpretation of NMR logs at in-situ conditions. Enhanced quantification of surface relaxivity also enhances NMR–based reservoir characterization and helps to improve the estimates of hydrocarbon reserves in organic–rich mudrocks.

Joint inversion of nuclear magnetic resonance data from partially saturated rocks using a triangular pore model

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. JM15-JM28 ◽  
Author(s):  
Thomas Hiller ◽  
Norbert Klitzsch
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Joint Inversion ◽  
Nmr Relaxation ◽  
Relaxation Data ◽  
Surface Relaxivity ◽  
Partially Saturated

Measurement of nuclear magnetic resonance (NMR) relaxation is a well-established laboratory/borehole method to characterize the storage and transport properties of rocks due to its direct sensitivity to the corresponding pore-fluid content (water/oil) and pore sizes. Using NMR, the correct estimation of, e.g., permeability strongly depends on the underlying pore model. Usually, one assumes spherical or cylindrical pores for interpreting NMR relaxation data. To obtain surface relaxivity and thus, the pore-size distribution, a calibration procedure by, e.g., mercury intrusion porosimetry or gas adsorption has to be used. Recently, a joint inversion approach was introduced that used NMR measurements at different capillary pressures/saturations (CPS) to derive surface relaxivity and pore-size distribution (PSD) simultaneously. We further extend this approach from a bundle of parallel cylindrical capillaries to capillaries with triangular cross sections. With this approach, it is possible to account for residual or trapped water within the pore corners/crevices of partially saturated pores. In addition, we have developed a method that allows determining the shape of these triangular capillaries by using NMR measurements at different levels of drainage and imbibition. We show the applicability of our approach on synthetic and measured data sets and determine how the combination of NMR and CPS significantly improves the interpretation of NMR relaxation data on fully and partially saturated porous media.

scholarly journals Measurement of pore sized microporous-mesoporous materials by time-domain nuclear magnetic resonance

BioResources ◽  
2020 ◽  
Vol 15 (1) ◽  
pp. 1407-1418
Author(s):  
Zhi-hong Zhao ◽  
Ming-hui Zhang ◽  
Wen-Jing Liu ◽  
Quan-teng Li
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Rate ◽  
Porous Materials ◽  
Pore Size ◽  
Mesoporous Materials ◽  
Time Domain ◽  
Surface Relaxation ◽  
Pore Surface ◽  
Anodized Aluminum

Time-domain nuclear magnetic resonance (TD NMR) technology has been used for pore detection in porous materials for a long time, but there are few pore detection methods for microporous-mesoporous materials. The surface of different materials is obtained by pore detection of known pore materials. Relaxation rate, which obtains aperture information, has an important practical significance for the application of time-domain NMR technology in the characterization of porous materials. In this study, the T2 peaks of pores of known pore size materials, namely zeolite molecular sieves (0.3 nm and 1 nm) and anodized aluminum porous membranes (30 nm and 90 nm), were used to calculate the pore surface relaxation of zeolite molecular sieve with 0.3 nm pore size and 1 nm pore size. The ratio of the rate of the surface is 3.379; the ratio of the pore surface relaxation ratio of the 30 nm and 90 nm apertures of the anodized aluminum porous film is 3.031. This result is very close to the pore size ratio, indicating that the surface relaxation rate of the same material is directly related to the pore size, while the T2 peak can qualitatively measure the pore size.

Relating nuclear magnetic resonance relaxation time distributions to void-size distributions for unconsolidated sand packs

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D461-D472 ◽  
Author(s):  
Kristina Keating ◽  
Samuel Falzone
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Relaxation Time ◽  
Magnetic Resonance ◽  
Diffusion Regime ◽  
Fast Diffusion ◽  
Size Distributions ◽  
Void Size ◽  
Surface Relaxivity ◽  
Grain Sizes ◽  
Nmr Data

Nuclear magnetic resonance (NMR) is used in near-surface geophysics to understand the pore-scale properties of geologic material. The interpretation of NMR data in geologic material assumes that the NMR relaxation time distribution ([Formula: see text]-distribution) is a linear transformation of the void-size distribution (VSD). This interpretation assumes fast diffusion and can be violated for materials with high surface relaxivity and/or large pores. We compared [Formula: see text]-distributions to VSDs using grain-size distributions (GSDs) as a proxy for VSDs. Measurements were collected on water-saturated sand packs with a range of grain sizes and surface relaxivities, such that some samples were expected to violate the fast diffusion assumption. Samples were prepared from silica sand with three different average grain sizes and were coated with the iron-oxide mineral hematite to vary the surface relaxivity. We found analytically that outside the fast diffusion regime, the [Formula: see text]-distributions are broader than in the fast diffusion regime, which could lead to misinterpretation of NMR data. The experimental results showed that the [Formula: see text]-distributions were not linear transformations of the GSDs. The GSDs were a single peak independent of the hematite coating. The [Formula: see text]-distributions were broader than the measured GSDs, and the center of the distribution depended on the coating. Using an equation that does not assume fast diffusion to transform the [Formula: see text]-distributions to NMR-estimated VSDs resulted in distributions that were centered on a single radius. However, our attempts to recover the VSDs, as estimated from laser particle size analysis, were unsuccessful; the NMR-estimated VSDs were broader and yielded average pore radii that were much smaller than expected. We found that our approach was useful for determining relative VSDs from [Formula: see text]-distributions; however, future research is needed to develop a method for calibrating the NMR-estimated VSDs for unconsolidated sands.

scholarly journals A nuclear magnetic resonance study of water in aggrecan solutions

2016 ◽  
Vol 3 (3) ◽  
pp. 150705 ◽  
Author(s):  
Richard J. Foster ◽  
Robin A. Damion ◽  
Thomas G. Baboolal ◽  
Stephen W. Smye ◽  
Michael E. Ries
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Rate ◽  
Activation Energies ◽  
Proton Nuclear Magnetic Resonance ◽  
Water Molecules ◽  
Transverse Relaxation Rate ◽  
Relaxation Rates ◽  
Transverse Relaxation ◽  
Nuclear Magnetic

Aggrecan, a highly charged macromolecule found in articular cartilage, was investigated in aqueous salt solutions with proton nuclear magnetic resonance. The longitudinal and transverse relaxation rates were determined at two different field strengths, 9.4 T and 0.5 T, for a range of temperatures and aggrecan concentrations. The diffusion coefficients of the water molecules were also measured as a function of temperature and aggrecan concentration, using a pulsed field gradient technique at 9.4 T. Assuming an Arrhenius relationship, the activation energies for the various relaxation processes and the translational motion of the water molecules were determined from temperature dependencies as a function of aggrecan concentration in the range 0–5.3% w/w. The longitudinal relaxation rate and inverse diffusion coefficient were approximately equally dependent on concentration and only increased by upto 20% from that of the salt solution. The transverse relaxation rate at high field demonstrated greatest concentration dependence, changing by an order of magnitude across the concentration range examined. We attribute this primarily to chemical exchange. Activation energies appeared to be approximately independent of aggrecan concentration, except for that of the low-field transverse relaxation rate, which decreased with concentration.

Improved Analysis of Nuclear-Magnetic-Resonance Measurements in Organic-Rich Mudrocks Through Experimental Quantification of the Hydrocarbon/Kerogen Intermolecular-Interfacial-Relaxation Mechanism

SPE Journal ◽  
2020 ◽  
Vol 25 (05) ◽  
pp. 2547-2563
Author(s):  
Saurabh Tandon ◽  
Zoya Heidari
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Analytical Model ◽  
Dipolar Coupling ◽  
Surface Relaxation ◽  
Experimental Measurements ◽  
Adsorption Theory ◽  
Surface Relaxivity ◽  
Cutoff Values ◽  
Intermolecular Coupling

Summary Nuclear-magnetic-resonance (NMR) measurements have become a popular choice for estimating hydrocarbon saturations in organic-rich mudrock reservoirs. Previous publications have shown that the dominant mechanism for surface relaxation during NMR measurements in organic pores is intramolecular dipolar coupling among hydrocarbon protons. However, the influence of kerogen/hydrocarbon intermolecular interactions and kerogen thermal maturity on the surface relaxivity has not been reliably quantified. The objectives of this paper are to experimentally quantify the influence of intermolecular coupling on kerogen surface relaxivities; compare the experimentally determined surface relaxivities with those obtained from our previously published analytical model; and quantify the effect of intermolecular coupling on estimates of the adsorbed-hydrocarbon phase volume in simple geometries. First, we selected two organic-rich mudrock formations with different kerogen thermal maturities and extracted pure kerogen from them. The extracted-kerogen samples were synthetically matured by increasing the temperature at 4°C/min from 25 to 450°C under a controlled environment. The petrophysical properties of kerogen samples at different thermal maturities were quantified using pyrolysis and Brunauer-Emmett-Teller (BET) measurements. The untreated and thermally mature kerogen samples were then saturated with protonated and partially deuterated chloroform mixtures. Consequently, we performed longitudinal (T1) and transverse (T2) measurements on the kerogen/chloroform mixtures. Then, we compared the surface relaxivities estimated from T1/T2 and BET surface-area measurements with those predicted by a previously published theoretical model derived from generalized adsorption theory. Finally, we performed a sensitivity study demonstrating the effect of intermolecular dipolar coupling on estimates of adsorbed-hydrocarbon volume by modeling kerogen pores as synthetic spherical objects. Results indicate that synthetic maturation of kerogen samples relatively increased their specific surface areas by up to 97.1%. When chloroform deuteration is kept constant and kerogen samples were heat treated from temperatures of 25 to 450°C, the T1 and T2 surface relaxivities relatively decreased by up to 70.1 and 80.3%, respectively. Our recently introduced analytical model was able to reliably quantify the kerogen surface relaxivities estimated from experimental measurements with a relative error of 30.5%. The results of the sensitivity analysis showed that improved assessment of kerogen surface relaxivity by including intermolecular coupling enhanced the NMR-based adsorbed-hydrocarbon-volume estimates relatively by up to 41.9% when kerogen pores were modeled as synthetic spherical objects. The results of the experimental measurements support the observations of the analytically developed surface-relaxivity model derived from the generalized adsorption theory. Accurately quantifying the mechanism contributing to surface relaxation helps in providing accurate temperature and frequency corrections for T2 and T1/T2 cutoff values. Such cutoff values can then be extended to in-situ conditions improving downhole estimates of NMR-based hydrocarbon saturations in organic-rich mudrocks.

Nuclear magnetic resonance surface relaxation mechanisms of kerogen

Geophysics ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. JM15-JM22 ◽  
Author(s):  
Boyang Zhang ◽  
Hugh Daigle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Relaxation Rate ◽  
Dipolar Coupling ◽  
Surface Relaxation ◽  
Proton Density ◽  
Transverse Relaxation Rate ◽  
Pore Fluids ◽  
Transverse Relaxation

Nuclear magnetic resonance (NMR) relaxometry is an excellent tool for probing the interactions between solid pore surface and pore fluids in porous media. Surface relaxation is a key component of NMR relaxation. It is well-known that in conventional rocks, paramagnetic centers contribute most to the surface relaxation phenomenon. However, the interactions between organic pore surfaces and pore fluids, and the mechanism of surface relaxation in organic shale pores, are not well-understood. We tackle the issue using deuterated compounds to adjust the proton density in the liquid phase and monitoring the transverse relaxation rate changes of kerogen-fluid mixtures. With the Barnett and Eagle Ford kerogen isolates, we found that for alkanes, it is intramolecular dipolar coupling that dominates among the magnetic interactions. As a result, the transverse relaxation rate of alkane proton spins is more likely to be dependent on the concentration of active adsorption sites on the kerogen surface, rather than the kerogen proton density. For water inside organic pores, surface relaxation most likely originates from hydrogen bonding and intermolecular dipolar coupling. We also examined the temperature effect on kerogen surface relaxation and found temperature-dependent behavior that is consistent with surface relaxation by hydrogen bonding and homonuclear dipolar coupling interactions.

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